In numerous contexts humans perform tasks by interacting with machines via actuators having knobs, dials or linear actuators. Such human interaction in many instances becomes conditioned upon the responsiveness of the actuator. The human operator interacts in accordance with tactile feedback perceived through contact with the actuator knobs, dials or handles.
For example, in video or film editing using systems as described in U.S. Pat. Nos. 4,937,685 and 4,964,004 which are incorporated herein by reference, an editor edits video image information at a console having a plurality of "control wheels" (i.e. large dials or knobs). The film or video editor controls operation of a composition system from an operator's console, as illustrated in FIG. 1, using two sets of controls, one for each hand, to control the editing process. Each control set includes a plurality of finger switches or pushbuttons 110 clustered proximate to a large rotatable control wheel 112, facilitating tactile operation with minimal hand movement. As the editor is focussing on at least one video monitor, viewing frames of visual source material during the editing function, it is generally the case that the operator will acquire a feel for the various controls and become acclimated to their functionality through tactile feedback therefrom, rather than having to look at the control wheel(s) for visual feedback. Accordingly, more efficient human interaction with, and sensitivity to the composition system is achieved.
The control wheels 112 exhibit tactile responsiveness, such as detents or clicks, as they are rotated. Typically, a full rotation of the wheel 112 is correlated to a unit of time, such as one second, of viewing the visual source material being edited. A corresponding number of "frames" of visual source material will be viewed during such a time period, depending on the medium or type of source material being edited. It is most desirable that the number of frames of source material be correlated to the tactile responsiveness, i.e. number of clicks, of the wheel 12 during rotation. For instance, film editing involves standardized source material of which twenty-four (24) frames are provided per second. Thus, it is most desirable that in a full rotation of the wheel 112 (presenting one second of source material), the wheel respond with twenty-four (24) clicks, each click corresponding to one frame of the visual source material.
While film editing involves source material having twenty-four (24) frames per second, other video medium standards require different frame rates. The frame rate, or number of frames per second according to the National Television System Committee (NTSC) is thirty (30) frames per second, a standard promulgated for television video in the United States. Standards such as PAL and SECAM provide for a standard frame rate of twenty-five (25) frames per second in England and France respectively. New standards for high definition television specify a frame rate of thirty (30) or sixty (60) frames per second.
Differing frame rate standards relating to visual source material and the nature of mechanical detents in actuators, presents the problem that multiple actuators are required to facilitate correlation between actuator tactile responsiveness and the various visual source material standards. As illustrated in FIG. 1a, actuators known in the art for providing tactile responsiveness typically incorporate a mechanical detent mechanism. A fixed number of clicks is provided by a spring loaded friction mechanism 111 coacting with a sprocket 113 having a fixed number of cogs or detents corresponding to the desired number of clicks per revolution. Therefore, an actuator having twenty-four fixed detents is required and dedicated for a film editing context, a thirty detent actuator is required for a NTSC video editing system, a twenty five detent actuator is required in the PAL or CCAM video editing context, etc. The plurality of actuators required limits the flexibility of visual source material composition systems and significantly increases the complexity, cost and hardware requirements of a flexible system.
In addition to the lack of flexibility of use of fixed mechanical detent actuators, such actuators disadvantageously become worn and suffer tactile responsiveness degradation over time. Other mechanically/spring loaded linear or rotary actuators suffer similar deficiencies.